If you want to open/close a backdoor port
then use the code shown below:

OPEN:
netsh firewall add portopening (Method) (Port) (Server Suffix)

CLOSE:
netsh firewall delete portopening (Method) (Port)

EXAMPLE:

OPEN:
netsh firewall add portopening TCP 80 Webserver
netsh firewall add portopening UDP 21 FTPserver

CLOSE:
netsh firewall add portopening ALL 21 FTPserver

MORE EXAMPLES:
TCP - Transmission Control Protocol (TCP).
UDP - User Datagram Protocol (UDP).
ALL - All protocols.